Based on the literatures published over the past fifty years, a brief review is given of the studies on anodic oxide growth on tantalum. It has been demonstrated clearly that the oxide growth involves highly complex and unprecedented processes of ionic transport to which no satisfactory theory has yet been presented. Thus, in amorphous oxide and in the presence of a high electric field of 10⁶-10⁷ V cm^-1 range, both Ta⁵⁺ and O^2- ions migrate in a highly correlated manner, with new oxide formation proceeding simultaneously at the oxide/electrolyte and metal/oxide interfaces. Further small amounts of electrolyte anions are incorporated into the oxide which, depending on their nature, may be immobile or mobile inwardly or outwardly. To date, such complex processes of ionic transport may be best explained, though only qualitatively, by a “liquid droplet” model presented recently by Mott. However, further insights into the nature of liquid droplets, whose formation is thought to be an elemental process of ionic transport, are apparently required in the eventual development of an integrated theory of ionic transport. It is emphasized that the tracer experiments, in which migrations or non-migrations of various foreign cationic or anionic tracers are studied and interpreted in terms of the role of high electric fields, acting either generally or locally, on the dissociation or non-dissociation of various structural units in the oxides, provide an important and effective rote towards the required understanding.